Fluid control valves are used in a wide variety of applications for causing and controlling motion of various components. Hydraulic fluid control valves and systems are used in such applications when relatively large forces are to be transmitted and controlled through such components.
One type of hydraulic fluid control valve is a sectional valve. A sectional valve may typically include a plurality of separate cast and machined metal working valve sections. Each valve section may include internal fluid passages, external ports, and spool bores with valve spools slidably disposed within the spool bores. The spool bores may include main control valve spool bores in which main control valve spools are slidably disposed, and compensator spool bores in which compensator spools are slidably disposed to maintain predetermined pressure drops across the main control spools or to otherwise control fluid pressure. The spool bores and the spools are precisely machined, so that the spools slide freely in the bores with minimal clearance and minimal fluid leakage between the spool and the bore.
The valve sections typically include precisely machined substantially planar or flat surfaces, and the valve sections are assembled together with the flat surfaces of adjacent sections contacting one another. Tie rod holes extend through the sections, and tie rods extend through the holes. A torque is applied to the tie rods to assemble the sections tightly together without fluid leakage between the sections. This assembly torque establishes a compressive load within the sections of the valve, and this compressive load may cause a distortion within the sections. This distortion may be particularly troublesome when the distortion occurs around a spool bore, because the diametrical clearance between the bore internal diameter and the spool outer diameter tends to be very small, for example in the range of 0.0002 of an inch. Excessive spool bore distortion can cause the spool to bind within the bore, which is detrimental to the operation of the hydraulic sectional valve. Because the diametrical clearance needs to be small to keep leakage around the spool to an acceptable level, increasing the diametrical clearance to allow for increased spool bore distortion may not always provide a valid solution to compensate for spool bore distortion that results from tie rod assembly torque.